1. Field of the Invention
The present invention relates to a zoom lens and imager apparatus to be suitably used on a small-sized apparatus having an imaging function, particularly a digital still camera, a camera-equipped cellular phone, a personal digital assistant (PDA) or the like.
2. Description of the Related Art
Recently, size reduction is further demanded for the imager apparatuses, such as digital still cameras, in the entirety thereof as size reduction proceeds in the imaging devices, such as CCDs (charge coupled devices), CMOSs (complementary metal oxide semiconductors) . Development has been made recently on those reduced in thickness upon being mounted to an imager apparatus by bending the optical path of a lens system into so-called a bending optical system.
As a zoom lens using a bending optical system, JP-A-2000-131610 describes a zoom lens structured with a first lens group having a positive refractive power, a second lens group having negative refractive power, a third lens group having a positive refractive power and a fourth lens group having a positive refractive power whereby magnification can be changed by moving the negative second lens group and the positive fourth lens group. In the zoom lens, the optical path is bent approximately 90 degrees by arranging a prism within the first lens group. Within the first lens group, a fixed positive lens group is arranged in back of the prism.
Because the use of a bending optical system can reduce the thickness upon being mounted to an imager apparatus as described above, the recent tendency is toward mounting on various imager apparatuses. Meanwhile, there is a demand for thickness and cost reduction in the market. For this reason, development is desired for a bending optical system structured favorable in terms of cost while being reduced in thickness. In order to reduce the cost, it can be considered to use a resin material for the lens. However, where a resin lens is used, temperature characteristics are structurally taken into account to a full extent because characteristic change is significant with temperature as compared to the glass lens. In the conventional bending optical systems, e.g. four-grouped zoom structure as described in JP-A-2000-131610, those are known which use resin lenses in the third or fourth lens group, for example. However, it can be considered to actively use resin lenses in other lens groups in an attempt to reduce the cost furthermore.